In some kinds of rotary machines, the shafts or spindles to carry the rotational motions are driven to rotate at superhigh speeds which reach 30,000 to 50,000 revolutions per minute in the case of some textile production equipment such as for example roving frames, spinning frames and throwing machines. Such a superhigh speed rotation of a shaft or spindle imposes various exacting requirements on the bearing mechanism to be used to support the shaft or spindle. One of these requirements is to cope with the wear and abrasion of the members and elements of the bearing mechanism which are subject to sliding and rolling frictions concomitant with the superhigh speed rotation of the shaft or spindle supported by the bearing mechanism.
A known bearing mechanism which has been used for supporting the spindle of a textile production equipment such as typically a yarn wrapping machine uses a journal bearing assembly which is largely made up of an ordinary ball bearing consisting of inner and outer race members and spherical bearing elements interposed between the inner and outer race members. The shaft or spindle to be supported by such a bearing assembly is directly contacted by the inner race member of the ball bearing is driven to rotate at a speed equal to the speed of rotation of the shaft or spindle supported by the journal bearing assembly and, for this reason, the maximum speed of rotation allowable of the shaft or spindle is limited by the wear and abrasion resistance of the ball bearing.
In the field of machine engineering, it is known that ball bearings in general tend to be critically worn out to such an extent as to be no longer serviceable when subjected to continuous rotation at speeds exceeding about 15,000 revolutions per minute. With the rotational mechanism in which the shaft or spindle is contacted by the inner race member of a ball bearing, therefore, the shaft or spindle must be driven for rotation at a speed lower than 15,000 revolutions per minute. This has brought forth a bar to increasing the performance efficiency or achieving the desired performance efficiency of, for example, a yarn wrapping machine.
To break through such a bar, a journal bearing assembly has been proposed, which is capable of withstanding the rotation at speeds higher than 30,000 revolutions per minute and maintaining a shaft, spindle or the like in a stable condition for an extended period of time.
A representative example of such a journal bearing assembly is shown in U.S. patent application Ser. No. 071,232. One of the outstanding features of the journal bearing assembly therein shown is the arrangement in which the revolution speed of the shaft or spindle supported by the bearing assembly is transmitted, upon reduction, to the rotary member of a bearing forming part of the bearing assembly so that the shaft or spindle can be driven to rotate at a speed higher in a desired ratio than the upper limit of the acceptable range of the revolution speed of the bearing assembly. The prior-art journal bearing assembly is constructed and arranged in such a manner that the loads imparted to the bearing assembly in radial directions from the shaft or spindle supported by the bearing assembly are cancelled by one another so that the shaft or spindle is maintained in a correct position with respect to the bearing assembly and is prevented from being caused to sway or laterally oscillate during superhigh speed rotation of the shaft or spindle. The prior-art bearing assembly is further constructed and arranged so that the impacts and vibrations which may be transferred to the bearing assembly from the shaft or spindle supported by the bearing assembly can be efficiently dampened out so that the shaft or spindle is enabled to rotate smoothly and noiselessly in the bearing assembly.
More particularly, the journal bearing assembly taught in U.S. patent application Ser. No. 071,232 comprises a casing, a bearing holder formed with a cavity therein and closely fitted in the casing and at least three bearing units retained in position in the cavity of the bearing holder and arranged in symmetry about the center axis of the cavity. Each of the bearing units comprises a rotatable member freely rotatable in the cavity about an axis parallel with the center axis of the cavity, an inner race member rotatable with the rotatable member, an outer race member fast on the bearing holder, and bearing elements rollably disposed between the inner and outer race members and wherein the shaft or spindle to be supported by the bearing assembly is in rollable contact with the respective rotatable members of the individual bearing units. If, therefore, the respective rotatable members of the individual bearing units are sized with respect to the spindle or a journal portion of the spindle in such a manner that the diameter of each of the rotatable members is a certain number of times larger than the journal portion of the spindle, each of the inner race members mounted on the rotatable member is to be driven for rotation with a number of turns per unit time which is smaller by the particular number of times than the number of turns of the spindle. If, for example, the spindle or the journal portion of the spindle has the diameter of 12 mm and the rotatable member of each of the bearing units has the diameter of 36 mm which is thrice larger than the diameter of the former and if the spindle is driven to make 40,000 turns per minute, each of the inner race members of each bearing unit will make about 13,333 turns per minute which is approximately equal to one third of the number of turns of the spindle. Such a revolution speed of the inner race members with respect to the stationary outer race members is within the range acceptable for bearings in general and will therefore assure the guaranteed performance quality and service life of the bearing unit.
To exploit these outstanding features and advantages of the prior-art journal bearing assembly, it is of critical importance that such a journal bearing assembly be used in combination with a thrust bearing unit which is competent in performance with the journal bearing assembly. A known thrust bearing unit using rolling elements of the ball or roller type is not capable of reliably carrying the axial load of the spindle or shaft supported by the prior-art journal bearing assembly of the described nature.
It is, accordingly, an object of the present invention to provide a bearing mechanism which includes a thrust bearing unit which is compatible in use with a journal bearing assembly withstanding the super-high rotation of a spindle or shaft to be driven for rotation at speeds of the order of tens of thousands of revolutions per minute.